我试图找出一个大数字的最大素数,当我运行这个我遇到一个错误说:
回溯(最近一次调用最后一次):文件“prb3.py”,第45行,在print prime_factor()文件“prb3.py”,第12行,在prime_factor中为n在范围(2,i)中:MemoryError
当我使用像13195这样的小编号运行时它工作正常
"""
Problem:
The prime factors of 13195 are 5, 7, 13 and 29.
What is the largest prime factor of the number 600851475143 ?
"""
import math
def prime_factor():
i=600851475143
factors=[] #list stores all the factors of a number
for n in range(2,i):
if(i%n==0 and (n%2!=0 and n!=2)):
factors.append(n)
"""
Now I have all the factors(which are not even numbers)
Next step is to find prime number from factors list
"""
for factor in factors:
sqr_root=int(math.sqrt(factor))
"""
I take a factor from list and divide it by numbers from 3
to sqroot(factor-1).If I get a 0 as remainder I consider it
as non prime and remove from the list.I apply this only to
factors whose sqr root is greater than 3.If it is less than
3 I divide it by each number between 3 and factor-1.
"""
if(sqr_root<=3):
for num in range(3,factor-1):
if(factor%num==0):
factors.remove(factor)
break
else:
for num in range(3,sqr_root):
if(factor%num==0):
1,1 Top
return len(factors)
if __name__ == "__main__":
print prime_factor()
1 回答
在Python2中,
range()
返回一个列表 . 在您的情况下,列表将包含600851475141 int对象 . 由于列表太大,它不能适合你的内存,所以你得到了内存错误由于您并不真的需要同时在内存中使用所有这些数字,因此您可以尝试使用
xrange()
.我认为您可以通过在找到它们时分解因素来简化您的问题 . 例如 .
不需要循环600851475141次可以使您的程序更快